The Naruto age question is so easy.
Of course he is as old as the other kids in his class.
And he didn't have to take 3 extra years in school because he failed 3 times.
You think the Shinobi school works just like a normal school, but it doesn't.
It actually works like a drivers license (the finals at least).
You fail the final exam, so you study a bit more and take it again after a few weeks.
It would be stupid to let him retake a whole years just because he failed the Bunshin exam.
They also wouldn't let Naruto take the test earlier. You saw how bad a student he was.
My reason for this theory.
Lee, Neji and Tenten are, as we know one year older than Naruto is.
If he failed and had to retake a years he would've been in their class for a whole years.
And so, at the chuunin exam, he had known who they are (and they who he is).
But they didn't know each other.
So he was never in class with them.
It's pretty obvious.
"For Feanor was made the mightiest in all parts of body and mind, in valour, in endurance, in beauty, in understanding, in skill, in strength and subtlety alike, of all the Children of Illuvatar, and a bright flame was in him"